Description

Northern flying squirrels are the primary prey of northern spotted owls and are important dispersers of fungal spores in Pacific Northwest forests. Despite the importance of these squirrels in forest ecosystems, information is lacking on life history and methods for determining age and reproductive condition. In the laboratory, we measured epiphyseal notch, femur length, rostrum length, least interorbital breadth, rump pelage length and color, and tail width of dead squirrels. We analyzed weight, pelage color, and reproduction for field-collected data from live squirrels. We also described age-class differences in facial features and tail size and shape in the Puget Trough. A birth-year-based age-class system had several advantages over the traditional juvenile-subadult-adult class system. Three age classes can be distinguished in the field, each with varying degrees of accuracy. Reproduction of northern flying squirrels can be reliably determined in live-trapping studies. Enlargement, turgidity, and redness of genitalia are detectable signs of reproductive activity, whereas reduction, flaccidity, and paleness signal inactivity for both males and females. Nipple length is the best indicator for distinguishing sexual maturity of inactive females. The most effective way to avoid mistakes and ambiguity about age and reproductive status in the field is to take descriptive notes. Maturation and reproductive patterns were similar among the Puget Trough, Olympic Peninsula, and northern Cascade studies in Washington. Squirrels in the Coast Range of Oregon, however, displayed different patterns. Regional populations differed in proportion of females reproductively active, the reproductive maturity of yearling females, and survivorship across age classes. Regional variations suggest accurate assessment of age and reproduction is a prerequisite for understanding flying squirrel ecology.